Approach:
The experimental site will be located within a 6 ha field on a private farm (45.72°Lat. N, -119.048 Lon. W) 20-km west of Pendleton, OR. The field experiment will consist of nine annual crop rotations (Table 3) planted in a RCB design. Annual crops will include winter wheat (WW), winter triticale (WT), winter oilseed (WO), spring wheat (SW), spring oilseed (SO), spring barley (SB), and spring triticale (ST). The WW-summer fallow (SF), WW-reduced tillage fallow (RTF), and WW-SB-RTF are established rotations that will serve as controls. Spring oilseed will be B. carinata to be obtained from Agrisoma through this agreement. Winter industrial B. napus rapeseed (cv. Durola) will be obtained from the Univ. of Idaho oilseed breeding program. The experimental design will be a randomized complete block with four replicates. Starting in fall 2013, each phase of each cropping sequence will be present in four replications each year for a total of 96 (96 = 24 × 4) plots. Tillage of SF plots will be done with traditional high-soil disturbance primary methods whereas tillage of RTF will be with wide blade sweeps and one or two rod weeding operations. All fertilizers will be banded at planting about 5 cm below and to the side of the seed row with a minimum disturbance Seed Hawk air drill. Winter cereal will be the initial crop in a sequence. Harvest index will be computed from seed yield and standing biomass. Grain protein concentration will be determined on subsamples with a dry combustion analyzer. Seed oil concentration will be determined with a nuclear magnetic resonance analyzer. Soil cores for gravimetric soil water and soil nitrogen (N) determinations will be collected in each plot by hydraulic probe at pre-plant and post-harvest to a depth 1.5 m in 0.3 m increments. Water budgets will be determined by calculating volumetric water from gravimetric water and soil bulk density. Plant water use will be calculated as pre-plant soil water plus rainfall minus post-harvest soil water. Water use efficiency will be calculated as grain yield and water use in ratio. It is assumed that surface water runoff and leaching of water below the root zone are negligible in this low rainfall environment. The nitrogen recovery index for different crops will be calculated by dividing grain N by total N supply. Total N supply is the sum of applied N, preplant soil N, and mineralized N over the growing season. Crop, soil, and weed data will be analyzed with PC-SAS using a repeated measures mixed ANOVA model. Crop rotation and soil depth will be considered as fixed effects whereas replication, crop rotation×replication, plot within crop rotation, and replication×plot within crop rotation will be random effects. Differences among treatments will be reported at the 0.05% level of significance. Regression residuals will be examined for normality, equal variances, and independence. The study will be conducted for a minimum of 6-yr to encompass two cycles of a 3-yr sequence, and detect a significant year effect and draw conclusions about grain quality and yield.